As polyamides, nylon 6, nylon 66 and the like have been heretofore widely known. Since these aliphatic polyamides have excellent moldability, they have been widely employed for automotive parts, electric or electronic parts and mechanical parts.
On the other hand, polyamide resins having high heat resistance have been enthusiastically developed, and a high heat-resistant resin composition comprising nylon 6T containing hexamethylene diamine and terephthalic acid as main components has been put into practical use.
In recent years, downsizing (reduction in weight, thickness and size) of electronic equipments, enhancement of performance (increase of frequency) thereof and making the electronic equipments portable (mobile, movable) have been rapidly promoted. With such promotion, high-density mounting technique of printed circuit boards (PCB) and reduction in size of the parts have become indispensable.
As the high-density mounting technique, surface-mount technique (SMT) is now widespread, and lead-free solder has come into wide use at the present day. Under such circumstances, higher heat resistance is required for the parts to be mounted, and with the reduction in size of the parts, higher flowability is required for the resins used for injection molded articles.
On the other hand, the resins for large-sized parts such as automotive parts need to have such high flowability that they can be filled in a cavity in the injection molding process, and besides, they also need to have excellent mold-releasing properties in order to prevent deformation due to lack of mold-releasing properties.
In case of the aforesaid polyamides, however, thermal deformation of the parts or melting of the resins sometimes takes place during the mounting process using SMT, or the polyamide resins are sometimes unsuitable for molding into automotive parts because of lack of flowability or stick in mold.
As high heat-resistant polyamide, nylon 46 is known, and its thermal deformation temperature is higher than that of the conventional polyamides. However, it has a problem that because of high water absorption, water contained in the resin is vaporized in the mounting process to cause blisters on the surface of the part.
Under such circumstances as mentioned above, the present inventors have proposed, in JP2763348B2 (U.S. Pat. No. 5,183,843), a polyamide resin composition comprising an aromatic polyamide, which comprises a dicarboxylic acid component (a) comprising terephthalic acid, an aromatic dicarboxylic acid other than the terephthalic acid and/or an aliphatic dicarboxylic acid of 4 to 20 carbon atoms, and a diamine component (b) comprising an aliphatic diamine and/or an alicyclic diamine, a fibrous reinforcement and a derivative of an aliphatic carboxylic acid of 26 to 32 carbon atoms.
Since the above polyamide resin composition is relatively excellent in heat resistance, rigidity, flowability, mold-releasing properties, etc., it is widely used as a molding material for electric or electronic parts and automotive parts.
If reduction in size of the parts used for PCB is promoted as described above, high flowability of the resin is desired in order to fill the resin into the end of the mold for the parts. The conventional polyamide resin compositions, however, have insufficient flowability, and hence they cannot be filled into the end of the mold for the parts in some cases.
Further, the conventional polyamide resin compositions are often reinforced with fibrous fillers such as glass fiber, and in this case, the flowability is sometimes deteriorated by the fibrous fillers. Accordingly, development of a polyamide resin composition having excellent heat resistance and also having high flowability and excellent mold-releasing properties has been desired, whether the resin contains a fibrous filler or not.